1. Field of the Invention
This invention relates to a manufacturing method for providing an embossed thermoplastic surface covering with a photopolymerized wear layer.
2. Description of the Prior Art
The desirability of protecting vinyl substrates such as thermoplastic vinyl-asbestos tile and decorative thermoplastic sheet goods utilized as floor coverings has been well recognized, and recently such substrates, protected by clear, tough, mar-resistant coatings, which are substantially 100% reactive and photocured have become widely available. For example, U.S. Pat. No. 3,485,732 has suggested radiation curable coating compositions for application to plastic substrates such as linoleum, and U.S. Pat. No. 3,924,023 suggests the application of photopolymerizable coatings to vinyl-asbestos substrates. It is substrates of the latter type, which have first been embossed, with which this invention is illustrated, although it will be readily evident that the invention has application in coating any embossed thermoplastic substrate.
It has been discovered that when an embossed vinyl substrate, particularly adapted for surface coverings such as floors, is coated with conventional, photopolymerizable coating compositions utilizing a curtain coater to apply the photopolymerizable coating to the substrate, the application of conventional coatings of about 2 to 5 mils results in the occlusion of air bubbles within the coating along the leading edge of the deeper valleys of the vinyl substrate, i.e., those edges which first pass beneath the curtain coater. Such bubbles can prove to be highly disadvantageous if they, in turn, are near or at the upper surface of the coating in that, should they puncture or break under wear conditions, they provide sites for dirt entrapment. Since the preferred coatings are essentially 100% reactive, they are generally highly viscous, and when subjected to an ultraviolet light cure, any occluded air will become permanently entrapped in the coating at the time of cure.